Electron tube structure and the manufacture thereof



June 1946 J. E. BEGGS 2,402,119

ELECTRON TUBE STRUCTURE AND THE MANUFACTURE THEREOF Filed Aug. 10, 1944 OCAPACITANCE Invent OT":

I M M James EBe 5,

mm by $4474?) His Attorney.

Patented June 18, 1946 ELECTRON TUBE STRUCTURE AND THE MANUFACTURE THEREOF James E. Bcggs, Schenectady, N. Y., asslgnor to General Electric Company, a corporation of New York Application August 10, 1944, Serial No. 548,859

E 13 Claims.

The present invention relates to electronic tube structures and to methods and apparatus used in the manufacture thereof.

It is known that in the use of electronic tubes for radio and high frequency circuits. the interelectrode capacitance of the tube and the total tube capacity have a considerable efiect on the operation of the tube and it is desirable in the design or such circuits, to have electron tubes with interelectrode capacitances which fall within a predetermined range and which are of a desired value. It is an object of the invention to provide an electron tube having an accurately adjusted electrical capacitance.

It is another object of the present invention to provide a new and improved method of adlusting the interelectrode capacitance of an electronic tube.

It is a further object of my invention to provide a new and improved apparatus for accurate- 1y spacing th electrodes in an electron tube.

It is still another object of my invention to provide a new and improved grid structure for an electron discharge device.

It is a still further object of my invention to provide a new and improved plane electrode assembly for an electron tube.

It is a still further object of my inventionto provide a new and improved arrangement for positioning the grid structure in an electronic tube.

A further object of my invention is to provide a new and improved method of spacing electrodes in an electron tube.

Still another object of my invention is to provide a new and improved capacitance measuring device which is not affected by changes in atmospheric conditions.

Briefly stated, in accordance with one aspect of my invention, I provide a new and improved planar grid structure for an electron tube and a method and an apparatus for assembling the grid structure into a tube by means or which, while the tube is beingassembled, the capacitance between a pair of electrodes is adjusted between narrow limits to a desired value. Alternatively. in accordance with another aspect of my invention, the total capacitance of the tube includin that of the seals and metallic parts thereof is adjusted to a predetermined value by controlling the spacing between a pair of electrodes to provide a tube particularly useful in radio frequency circuits. A capacitance measuring device. which uses air as its sole dielectric and which i not affected by changes in temperature and humidity conditions is employed to insure the precise value of capacitance for the tube. Claims directed to my improved method and apparatus for manufacturing electron discharge devices are presented in my divisional application Serial No. 604,676. filed July 12, 1945, and assigned to the assignee of this application.

For a better understanding of my invention, reference may be had to the following description taken in connection with the accompanying drawing and its scope will be pointed out in. the appended claims. Fig. l of the drawing i a vertical sectional view of a portion of an electron tube embodying the invention; Fig. 2 illustrates the grid structure and a tool used in its assembly into a tube; Figs. 3 and e are perspective views of grid structures which may be employed in the tube of Fig. 1; Fig. 5 is a perspective view of apparatus used in assembling the portion of the electron tube shown in Fig. l; and Fig. 6 is a sectional view of a portion or the apparatus of Fig. 5..

Referring particularly to Fig. i, there is shown a portion of an electronic tube having an anode shell I and a grid shell 2 maintained in spaced relation by a vitreous cylinder 3 sealed between opposing flanged portions of the shells. The shells I and 2 are formed preferably of a suitable metallic material, such as copper or silver-plated steel. and the seal 3 is formed of a suitable insulating material which wets with the plating of the members i and 2, such as for example a bore silicate glass. The anode shell i is hollow and has a neck portion 4 which terminates in an active shade or electron receiving portion 5. Positioned within the grid shell 2, in a manner to I be explained more in detail hereinafter, is a grid assembly comprising a tubular conductive member 5 flared inwardly at its upper end to form a flange 1 across which is secured a grid 8. The cylinder 8 around its outer periphery is provided with a plurality of ridges or corrugations 8 which maintain the cylinder 8 in a desired position within the grid shell 2 during assembly operation.

In Fig. 2 the grid cylinder. 8 is shown in position on a stud l0 used in adjusting the position of the grid assembly within the grid shell 2. Fig. 3 is a perspective view of the grid assembly shown in Figs. 1 and 2 and illustrates more clearly the corrugations 9 on the tube 6 and the dance 1 across which is stretched a mesh grid 8. The grid 8, preferably while it is' under tension, is soldered to the upper face of the flange I during the construction of the grid assembly.

Fig. 4 show an alternative grid assembly for use in a tube having planar electrodes and which comprises a grid cylinder having a plurality of serrations or louvers i2 and a flange l3 at its upper end. A circular washer M having a central opening l5 has soldered thereto a plurality of closely spaced parallel grid wires I6. Preferably, the grid wires i6 are united to the washer Hi, as by soldering, and thereafter the composite grid washer structure is placed upon the flange l3 and attached thereto as by welding.

In Fig. 5 there is hown apparatus particularly useful in assembling the portion of the tube structure shown in Fig. 1 to obtain predetermined spacing between the anode surface 5 and the grid 8 to provide a desired capacitance between these electrodes. The apparatus of Fig. 5 includes a base portion l which contains a source of unidirectional potential and a. capacitance bridge not shown). A press l8 supported upon the base IT includes a base portion i9 upon which is mounted a block of insulation material which carries the stud l0, and a reciprocating plunger 2| secured to the lower portion of a rack member 22. Th rack member 22 engages a driving pinion (not shown) in the head 23 of the press and is actuated by means of a lever 24. The vertical movement of the plunger 2| may be measured by means of a suitable micrometer 25. The plunger 2| is adapted to fit into the anode shell to place the grid shell 2 over the grid cylinder 6, the latter being supported on the stud l0. Electric connection to the plunger 2| for purposes to be pointed out later is made by means of a lead 26 which is grounded to the press I8.

Located in the base portion IQ of the' press is a sleeve 27 for receiving a capacitance rod and a stop 28 for limiting the motion of that rod. This portion of the apparatus is shown in enlarged sectional view in Fig. 6, the capacitance rod 29 being shown in position within the lefthand sleeve 21 and the right-hand sleeve 30 and abutted against the stop 28. The capacitance rod 29 has an intermediate portion 3| of reduced diameter connecting two portions of larger diameter which are machined to make a good fit with the inner surface of the sleeves 21 and 30. C0- operatin with the intermediate portion 3| to form therewith an air core capacitance is an annular metallic. member 32 attached to a stud 33 which is in screw-threaded engagement with the stud l0 and supported from the block 20 of insulating material. The fixed annular electrode 32 has a central aperture which likewise is of the inner diameter of the sleeves 2! and 30 so that, in positioning the capacitance rod 29 in the sleeves 21 and 30, the right-hand end of the rod passes through the opening of the electrode 32 to check its concentricity with the mov able electrode 3| of the capacitance. The fixed electrode 32, which is maintained at a positive potential, is connected by means of a lead 34 to a capacitance bridge 35 supplied with operating potential from any suitable source represented conventionally by the battery 36. The capacitance bridge 35 is of conventional form and the details thereof are not shown in the drawing. Th bridge includes a meter 31 connected across opposite points of the arms thereof in the usual manner. The capacitance formed by the electrodes 3|, 32 is connected in one of the arms of the capacitance bridge 35 in a well known manner and is in parallel with the fixed capacitance of the press Hi.

In the operation of the apparatus shown in Figs. 5 and 6 to obtain a desired interelectrode capacitance of an electron tube, according to one method, first, a capacitance rod, having an in termediate section 3| of a diameter sufiicient to form with the electrode 32 the exact value of capacity which is desired for an electronic tube, is placed in position in the sleeves 21 and 30 and the reading of the meter 31 is noted. Thereafter, the rod 29 is removed, a grid cylinder 5 is placed on the stud I0, an anode and grid shell assembly is placed over the grid cylinder, and the plunger 2| is lowered by means of a lever 24. It is apparent that the stud l0, which is at the same electrical potential a the electrode 32, is insulated from the grounded plunger 2| of the press M3 by the vitreous cylinder 3 of the electron tube structure. A capacitance, therefore, is formed between the anode shell and the grid shell and cylinder, which capacitance is substituted for the known capacity of the electrodes 3|, 32 in the same arm of the capacitance bridge. As the plunger 2| is lowered, the reading of the meter 31 is noted until a deflection is obtained which is the same as that obtained with the standard capacity of the electrodes 3|, 32 present in the bridge arm. Since the interelectrode capacitance of the tube assembly is substituted for the previous standard capacity, when the same reading is obtained, the interelectrode capacit is fixed at the desired value. It is apparent that, with this particular method of adjusting the capacitance, the presence of any capacitance of the press and Wiring is balanced out for the two readings. During the positioning of the grid cylinder in the grid shell 2, the corrugations or ridges 9 or the spring fingers l2, as the case may be, by engaging the inner walls of shell 2 support the cylinder 6 or II therein. When a desired interelectrode spacing is obtained the tube structure is removed from the press l8 and the grid cylinder is spot-welded in place.

The above-described method for obtaining a desired interelectrode capacitance is particularly useful in constructing an electronic tube for low frequency purposes, where the interelectrode capacitance includes the effect of seals, the envelope, and other portions of the tube. For tubes constructed for high frequency work, where the seal formed by the dielectric cylinder 3 may be displaced from the active electrode parts by a distance that is an appreciable portion of a wave length and its presence has little or no effect upon the desired value of interelectrode capacitance, the following method of assembling a tube, which balances out the capacitance due to the presence of the seals and envelope of a tube, is of importance. In this method, with a capacitance rod 29 inserted to give a desired interelectrode capacitance across the capacitance bridge arm, the grid cylinder 6 is placed in position on a stud i0 and an anod grid assembly is placed thereover and located by means of the plunger 2| until the active anode surface 5 and the grid 8 are separated by a substantial distance. In this manner the capacity of the fixed tube elements is connected in parallel with the stand ard reference capacity. The capacitance bridge is then adjusted to give a desired deflection on the meter 31, preferably a mid-scale reading. The arbitrary reading thus obtained includes both the fixed capacities of the tube elements and the standard capacity between the electrodes 3|, 32. The rod 29 is then removed to remove the standard capacity from the bridge arm and an interelectrode capacitance of the same value is substituted therefor by lowering plunger 2| to bring the grid 8 closer to sole dielectric electrodes 3|, 32 is the same as that which exists between the anode surface 5 and the grid 8 so that the capacity setting is independent of teming its construction,

5 I the anode surface 5 until thesame deflection of meter 31 is obtained. This gives a true measurement of the capacitance anisting solely .between the grid 8 andthe anode surface 5'. the value of which it is desired to set v equal to the known standard or reference capacity.

Inthe use of the apparatus for positioning the electrodes-in tubes, standard capacity elements or'rods 29 having intermediate portions ll of V diflerentdiameters of course maybe employed to obtain different ginterelectrode capacities of thetubes. oneof the'important features of the capacity balancing device is the fact that the which exists betweenthe active perature and humidity conditions. This dielectrlc, being air, is a relatively stable one. The eiiect of the dielectric block formed of a material which ordinarily is effected by tempera ture and humidity is balanced out for all measurements. Another advantage of the use of the a paratusshown is that each electronic tube, duris adjusted to give the exact value of-interelectrode capacitance desired. This value may take. into account either the presence of the seals and envelope of the tube or may balance outthe efiect of these elements of the tube.

In some cases it may be desirable to assemble tubes according to the .physical'spacing between the anode and grid, rather than to obtain a desired interelectrode capacitance. For such cases also, the apparatus of Fig. 5 may be employed, the micrometer 25 being used to measure the spacing between electrodes. The grid-to-anode spacing may be alternatively established by means of high frequency resonant circuits or any other desired means. It has been found that in the use of this particular apparatus and method for assembling electronic tubes, tubes have been manufactured which approach more closely to a desired uniform characteristic than those manufactured by any other apparatus or method heretofore employed.

While I have shown a particular embodiment of my invention, it will of course be understood that I do not wish to be limited thereto since various modifications may be made and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure bi Letters Patent of the-United States is:

1. A grid structure for an electronic tube having a cylindrical grid support comprising a hollow conductive cylinder having an inwardly directed flange at one of its ends, a plurality of clowy spaced grid wires stretched between opposite sides of said flange and attached thereto, said cylinder having longitudinally extending deformations for e the walls of said cylindrical support.

2. A grid structure for an electronic tube comprising a hollow conductive cylinder having an inwardly directed flange portion at one end thereof, a metallic disk secured to said flange portion, said disk having a centrally located aperture therein, and a plurality of closely spaced grid wires stretched across said aperture and attached between said disk and. said flange, said cylinder having longitudinally extending means for faciltating positioning thereof in an electron tube.

. opposite en eter cylinder and a centrally located aperture, said disk having a plurality of closely spaced grid wires planar electrode :mmber spaced from said surface and axially p 3. A grid structure for an electron tube comprising a hollow conductive cylinder having an inwardly directed flange at one end and a plurality of longitudinal slots extending from the a thin metallic disk having a diamsubstantialLv equal to the diameter of said stretched across said aperture, said disk and said wires attached to said flange.

4. The combination, in an electron tube. of a surface, a hollow cylindrical alined therewitlb'a grid structure comprising a hollow metal cylinder having an inwardly directed flange at one end and a plurality of closely spaced grid wires stretched across said flange and secured thereto, means adjustably supporting said grid in said cylindrical member with said flange parallel to said surface including a plurality of deformations on the metal cylinder engaging the inner wall of said metal member.

5. The combination, in an electron tube. of a planar electrode surface, a cylindrical shell axially aligned with said surface, insulating means supporting said shell in spaced relation with said surface, and a grid electrode supported within said shell, said electrode comprising a hollow cylindrical member having a plurality of closely spaced-grid wires stretched across the end thereof adjacent said surface, the surface of said hollow cylindrical member having longitudinally extending, deformations engaging the inner wall of said shell.

other member for adiustably supporting said grid structure therein.

7..Ihe combination, in an electron tube having an annular member forming a portion of the enclosure thereof, of an electrode adjustably supported within said annular member comprising a cylindrical conductive member having electrode means at one end thereof, said member having a pluralityof longitudinally extending louvers adjustably supporting said member within said annular member.

,8. The combination, in an electron tube having an annular metallic supporting member, of an electrode adlustably supported within said annular member comprising a hollow cylindrical conductive member having a plurality of closely spaced grid wires stretched across on end thereof, the outer diameter of said conductive member being substantially equal to the inner diameter of said annular member, whereby said conductive member may be adjustably positioned within said annular member and secured thereto.

9. The combination, in an electron tube having an annular metallic supporting member which forms a part of the envelope of said tube, of an electrode adjustably supported within said annular member comprising a hollow cylindrical conductive member having a plurality of clomly aaoai 1a 7 spaced grid wires stretched across one end thereof, the outer diameter of said conductive member lacin substantially equal to the inner diameter of said annular member, whereby said conductive member may be adjustably positioned within said annular member.

10. The combination. in an electron tube having a planar circular electrode and an annular supporting member in substantial coaxial alignment with said electrode, of a second electrode adjustably supported within said annular member comprising a hollow cylindrical conductive member having a plurality of closely spaced grid wires stretched across one end thereof, said conduetive member having means integral therewith for resiliently engaging the inner surface of said annular member. I

11. In an electric discharg device, a cylinder of insulating material, an anode structure sealed to one end of said cylinder and presenting a planar surface to the interior of said cylinder I and substantially perpendicular to the axis thereof, a metallic cylinder sealed to the other end of said cylinder of insulatin material, and a grid structure received within said metallic cylinder including a cylindrical portion slidably supported an electrode sealed to within and engaging the interior of said metallic cylinder and a planar portion substantially parallel to said planar surface.

12. In an electric discharge device. an envelope including a. metal cylinder and a cylinder of insulating material sealed in end-to-end relation,

the other end of said cylinder of insulating material and presenting a planar surface to the interior of said cylinder, and a grid structure received within said metallic cylinder including a cylindrical portion supported from the interior wall of said metallic cylinder and a planar portion substantially parallel to said electrode surface.

13. In an electric discharge device. an envelope including a metal cylinder and a cylinder of insulating material sealed in end-to-end relation, an electrod sealed to the other end of said cylinder of insulating material and presenting a planar surface to th interior of said cylinder, and a grid structure received within said metallic cylinder including a cylindrical portion having resilient engagement with the interior of said metallic cylinder and a planar portion substantially parallel to said electrode surface.

JAMES E. BEGGS. 

